The present invention relates to a planetary gearbox, in particular for a wind power plant.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Planetary gearboxes are used for example as transmission gearboxes to convert a low speed from a drive shaft of the planetary gearbox into a significantly higher speed of an output shaft of the planetary gearbox. Accordingly, planetary gearboxes are frequently installed in wind power plants, where a low speed of the rotor shaft has to be converted into a significantly higher speed of the generator shaft. With the use in wind power plants, planetary gearboxes are operated under very changeable operating conditions due to variable wind conditions. As a result of temporarily extremely low speeds of the drive shaft and at the same time extremely high force effect on the bearing, roller bearings are predominantly installed in planetary gearboxes for wind power plants in order to mount the planetary wheels.
Another approach involves the use of planetary wheel bearings in the form of slide bearings in planetary gearboxes for wind power plants. An example is disclosed in EP 2 383 480 A1 which describes a planetary gearbox having a gearbox housing, in which a central sun wheel with an external toothing is held for rotation about a central gearbox axis of rotation. Furthermore, a hollow wheel with an internal toothing is provided in the gearbox housing concentrically to the central gearbox axis of rotation. A planetary carrier is mounted in the gearbox housing so as to be able to rotate about the central gearbox axis of rotation. A number of planetary wheels are held on the planetary carrier. The planetary wheels have external toothings, which engage with the internal toothing of the hollow wheel and the external toothing of the sun wheel.
The planetary wheels are mounted on planetary wheel bearings configured as radial slide bearings so as to be able to rotate about planetary wheel axes of rotation. For a reliable operation of a radial slide bearing, its bearing clearance must also take into account that during the operation of the radial slide bearing, temperature and/or load-specific extensions and/or deformations may occur. The components of the radial slide bearing and/or the running surfaces of the mounted planetary wheels must therefore be manufactured with high precision, i.e. slight manufacturing tolerances, and/or refinished during assembly, which is associated with high costs.
During operation of the radial slide bearing, the bearing clearance gradually changes as a result of wear, which may result in a malfunction or failure of the radial slide bearing. Regular maintenance and, if necessary, replacement of the radial slide bearing is therefore necessary, when the bearing clearance of the radial slide bearing is about to be outside of an admissible range. This is accompanied by corresponding down times, in particular when wind power plants are involved.
Radial slide bearings can only dissipate radial forces. In order to also guide the planetary wheels axially and to prevent axial movements of the planetary wheels, axial slide bearings are also required, which dissipate axial forces acting on the planetary wheels. Such axial slide bearings can be embodied for instance in the contact range between the sides of the planetary carrier and the end faces of the planetary wheels and increase costs of such planetary wheel bearings.
It would therefore be desirable and advantageous to provide an improved planetary gearbox which obviates prior art shortcomings while being simple in construction and yet reliable in operation.